(1) Field of the Invention
The present invention relates to a picture display using an area light source such as a light-emitting diode array. More particularly, it relates to a picture display suitable for a stereoscopic display which makes it possible to watch three-dimensional images using binocular disparity by performing projection on the same screen by using a left and right pair of projectors without using special glasses.
(2) Description of the Prior Art
In general, a device configuration whereby a light valve is illuminated, and a modulated image signal is projected through a projection lens onto a screen is referred to as a projector. A device including this projector and a screen is referred to as a picture display.
A picture display using an area light source such as a light-emitting diode array is disclosed in the art, for example, Japanese Laid-Open Patent Publication No. 2000-56410. The projector herein shown is so configured that a luminous flux emitted from an area light source illuminates an light valve such as an LCD, and a modulated image signal is projected through a projection lens onto a screen. Further, with this picture display, the light beams emitted from red, green, and blue three color light sources are subjected to color recombination on a screen, thereby to perform color display by a single light valve, resulting in a lower cost.
With the prior-art picture display, a collimated luminous flux is emitted form each area light source. Therefore, when the area light source does not match in size with the light valve, i.e., when the luminous flux is smaller than the area of the light valve, there occur non-illuminated portions in the light valve to cause a picture defect. In contrast, when the luminous flux is larger than the area of the light valve, there occurs an ineffective luminous flux not incident upon the light valve, resulting in a reduced optical efficiency.
Further, with the prior art described above, the luminance uniformity of each area light source nearly matches with the luminous flux which illuminates the light valve. Accordingly, there has occurred the following problem. Namely, if light emissions from respective area light sources are not uniform, the light valve is unevenly illuminated. As a result, a lack of luminance uniformity occurs in a projected image. Further, the area light source itself is required to have a more higher mechanics in order to achieve the evenness of the luminance uniformity of the area light source.
In view of the foregoing circumstances, it is therefore an object of the present invention to enhance the optical efficiency regardless of the size of a light valve, and enhance the uniformity of the luminance of a projected image in a display using an area light source.
The present inventors have conducted various experiments and studies to attain the foregoing object. As a result, they have obtained the following unexpected finding. In general, this type of display is made up of a projector, and a screen for displaying a projected image projected from the projector. In the projector, an illumination lens is disposed between a light source and a light valve. In such a configuration, if the light valve is at least positioned roughly at the focus point of the illumination lens, extremely favorable results are obtained with respect to both the optical efficiency and the uniformity of the luminance of an image projected onto the screen.
Further, they have also obtained the following important finding. Namely, if the light source is also located at a position in a symmetrical relation to the light valve with respect to the illumination lens centrally interposed therebetween, and roughly at the focus point of the illumination lens, further more favorable results can be obtained.
The present invention has been completed based on such important findings. Below, the features of the display in accordance with the present invention will be described.
A display in accordance with a first aspect of the present invention in order to attain the foregoing object, comprises: a projector including a light source extending at least one-dimensionally or two-dimensionally, an illumination lens through which a luminous flux emitted from the light source passes, a light valve for modulating the luminous flux passed through the illumination lens, and a projection lens for projecting the luminous flux modulated at the light valve; and a screen for displaying a projected image projected by the projection lens of the projector, and it is characterized in that the light valve of the projector is located roughly at a focus point f of the illumination lens.
A display in accordance with a second aspect of the present invention in order to attain the foregoing object, is characterized in that the light source is located roughly at the opposite focus point of the illumination lens from the focus point on which the light valve is located.
A stereoscopic display in accordance with a third aspect of the present invention in order to attain the foregoing object, comprises: a left and right pair of projectors each including a light source extending at least one-dimensionally or two-dimensionally, an illumination lens through which a luminous flux emitted from the light source passes, a light valve for modulating the luminous flux passed through the illumination lens, and a projection lens for projecting the luminous flux modulated at the light valve; and a screen for displaying respective projected images projected by the projection lenses of the pair of the projectors on the same panel, and it is characterized in that the light valve of each of the projectors is located roughly at a focus point f of the illumination lens.
As described above, the light valve, and further the light source are respectively positioned roughly at the focus points f of the illumination lens. This is attributable to the following fact. Namely, if the deviation from the focus point f is within about xc2x125% range, although a little difference occurs in terms of its effects, the shift does not matter in terms of practicality, and is acceptable.
Further, in the case where the area of the light source is large, satisfying the relationship of the following expression (7):
W greater than 1.2f/Fnxe2x80x83xe2x80x83(7) 
where Fn denotes the F-number of the projection lens, f denotes the focal length of the illumination lens, and W denotes the diameter of the light source, the light source can be positioned at a distance in the range of from zero to 3.5 times the focal length f of the illumination lens away from the illumination lens.
In the case where the area of the light source is small, satisfying the relationship of the following expression (8):
Wxe2x89xa61.2f/Fnxe2x80x83xe2x80x83(8) 
the light source can be positioned at a distance of the focal length f of the illumination lens with a deviation within the xe2x88x9240% to +80% range away from the illumination lens.